The present invention relates generally to an optical apparatus, and more particularly to an optical apparatus comprises, for instance, an optical system for making visual observations or an image pickup optical system.
For a Keplerian finder used with digital cameras, etc., it is required to gain diopter control according to the diopter of an observer. In a prior art finder comprising an objective lens 902, a Porro II prism 903 and an eyepiece lens 901 as shown in FIG. 80, this is carried out by the back-and-forth movement of the eyepiece lens 901 for the reason mentioned above. However, one grave problem with this is that there must be some space for the mechanical structure needed for the back-and-forth movement of the lens.